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<title>Associative Sequence</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="fusion.sequence.concepts.associative_sequence"></a><a class="link" href="associative_sequence.html" title="Associative Sequence">Associative
        Sequence</a>
</h4></div></div></div>
<h6>
<a name="fusion.sequence.concepts.associative_sequence.h0"></a>
          <span class="phrase"><a name="fusion.sequence.concepts.associative_sequence.description"></a></span><a class="link" href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.description">Description</a>
        </h6>
<p>
          An Associative Sequence allows efficient retrieval of elements based on
          keys. Like associative sequences in <a href="http://www.boost.org/libs/mpl" target="_top">MPL</a>,
          and unlike associative containers in <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>,
          Fusion associative sequences have no implied ordering relation. Instead,
          type identity is used to impose an equivalence relation on keys. Keys are
          not checked for uniqueness.
        </p>
<div class="variablelist">
<p class="title"><b>Notation</b></p>
<dl class="variablelist">
<dt><span class="term"><code class="computeroutput"><span class="identifier">s</span></code></span></dt>
<dd><p>
                An Associative Sequence
              </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">S</span></code></span></dt>
<dd><p>
                An Associative Sequence type
              </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">K</span></code></span></dt>
<dd><p>
                An arbitrary <span class="emphasis"><em>key</em></span> type
              </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">o</span></code></span></dt>
<dd><p>
                An arbitrary object
              </p></dd>
<dt><span class="term"><code class="computeroutput"><span class="identifier">e</span></code></span></dt>
<dd><p>
                A Sequence element
              </p></dd>
</dl>
</div>
<h6>
<a name="fusion.sequence.concepts.associative_sequence.h1"></a>
          <span class="phrase"><a name="fusion.sequence.concepts.associative_sequence.valid_expressions"></a></span><a class="link" href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.valid_expressions">Valid
          Expressions</a>
        </h6>
<p>
          For any Associative Sequence the following expressions must be valid:
        </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                  <p>
                    Expression
                  </p>
                </th>
<th>
                  <p>
                    Return type
                  </p>
                </th>
<th>
                  <p>
                    Type Requirements
                  </p>
                </th>
<th>
                  <p>
                    Runtime Complexity
                  </p>
                </th>
</tr></thead>
<tbody>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><a class="link" href="../intrinsic/functions/has_key.html" title="has_key"><code class="computeroutput"><span class="identifier">has_key</span></code></a><span class="special">&lt;</span><span class="identifier">K</span><span class="special">&gt;(</span><span class="identifier">s</span><span class="special">)</span></code>
                  </p>
                </td>
<td>
                  <p>
                    <a href="http://www.boost.org/libs/mpl/doc/refmanual/integral-constant.html" target="_top">MPL
                    Boolean Constant</a>. Convertible to bool.
                  </p>
                </td>
<td>
                </td>
<td>
                  <p>
                    Constant
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><a class="link" href="../intrinsic/functions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">at_key</span></code></a><span class="special">&lt;</span><span class="identifier">K</span><span class="special">&gt;(</span><span class="identifier">s</span><span class="special">)</span></code>
                  </p>
                </td>
<td>
                  <p>
                    Any type
                  </p>
                </td>
<td>
                </td>
<td>
                  <p>
                    Constant
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><a class="link" href="../intrinsic/functions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">at_key</span></code></a><span class="special">&lt;</span><span class="identifier">K</span><span class="special">&gt;(</span><span class="identifier">s</span><span class="special">)</span>
                    <span class="special">=</span> <span class="identifier">o</span></code>
                  </p>
                </td>
<td>
                  <p>
                    Any type
                  </p>
                </td>
<td>
                  <p>
                    <code class="computeroutput"><span class="identifier">s</span></code> is mutable
                    and <code class="computeroutput"><span class="identifier">e</span> <span class="special">=</span>
                    <span class="identifier">o</span></code>, where <code class="computeroutput"><span class="identifier">e</span></code> is the first element in the
                    sequence, is a valid expression.
                  </p>
                </td>
<td>
                  <p>
                    Constant
                  </p>
                </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="fusion.sequence.concepts.associative_sequence.h2"></a>
          <span class="phrase"><a name="fusion.sequence.concepts.associative_sequence.result_type_expressions"></a></span><a class="link" href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.result_type_expressions">Result
          Type Expressions</a>
        </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                  <p>
                    Expression
                  </p>
                </th>
<th>
                  <p>
                    Compile Time Complexity
                  </p>
                </th>
</tr></thead>
<tbody>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><a class="link" href="../intrinsic/metafunctions/has_key.html" title="has_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">has_key</span></code></a><span class="special">&lt;</span><span class="identifier">S</span><span class="special">,</span>
                    <span class="identifier">K</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
                  </p>
                </td>
<td>
                  <p>
                    Amortized constant time
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><a class="link" href="../intrinsic/metafunctions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></code></a><span class="special">&lt;</span><span class="identifier">S</span><span class="special">,</span>
                    <span class="identifier">K</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
                  </p>
                </td>
<td>
                  <p>
                    Amortized constant time
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><a class="link" href="../intrinsic/metafunctions/value_at_key.html" title="value_at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">value_at_key</span></code></a><span class="special">&lt;</span><span class="identifier">S</span><span class="special">,</span> <span class="identifier">K</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
                  </p>
                </td>
<td>
                  <p>
                    Amortized constant time
                  </p>
                </td>
</tr>
</tbody>
</table></div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
            <code class="computeroutput"><a class="link" href="../intrinsic/metafunctions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></code></a><span class="special">&lt;</span><span class="identifier">S</span><span class="special">,</span> <span class="identifier">K</span><span class="special">&gt;</span></code>
            returns the actual type returned by <code class="computeroutput"><a class="link" href="../intrinsic/functions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">at_key</span></code></a><span class="special">&lt;</span><span class="identifier">K</span><span class="special">&gt;(</span><span class="identifier">s</span><span class="special">)</span></code>.
            In most cases, this is a reference. Hence, there is no way to know the
            exact element type using <code class="computeroutput"><a class="link" href="../intrinsic/metafunctions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">at_key</span></code></a><span class="special">&lt;</span><span class="identifier">S</span><span class="special">,</span> <span class="identifier">K</span><span class="special">&gt;</span></code>.The
            element at <code class="computeroutput"><span class="identifier">K</span></code> may actually
            be a reference to begin with. For this purpose, you can use <code class="computeroutput"><a class="link" href="../intrinsic/metafunctions/value_at_key.html" title="value_at_key"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">value_at_key</span></code></a><span class="special">&lt;</span><span class="identifier">S</span><span class="special">,</span> <span class="identifier">K</span><span class="special">&gt;</span></code>.
          </p></td></tr>
</table></div>
<h6>
<a name="fusion.sequence.concepts.associative_sequence.h3"></a>
          <span class="phrase"><a name="fusion.sequence.concepts.associative_sequence.expression_semantics"></a></span><a class="link" href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.expression_semantics">Expression
          Semantics</a>
        </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                  <p>
                    Expression
                  </p>
                </th>
<th>
                  <p>
                    Semantics
                  </p>
                </th>
</tr></thead>
<tbody>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><a class="link" href="../intrinsic/functions/has_key.html" title="has_key"><code class="computeroutput"><span class="identifier">has_key</span></code></a><span class="special">&lt;</span><span class="identifier">K</span><span class="special">&gt;(</span><span class="identifier">s</span><span class="special">)</span></code>
                  </p>
                </td>
<td>
                  <p>
                    A boolean Integral Constant <code class="computeroutput"><span class="identifier">c</span></code>
                    such that <code class="computeroutput"><span class="identifier">c</span><span class="special">::</span><span class="identifier">value</span> <span class="special">==</span>
                    <span class="keyword">true</span></code> if and only if there
                    is one or more elements with the key <code class="computeroutput"><span class="identifier">k</span></code>
                    in <code class="computeroutput"><span class="identifier">s</span></code>; see <a class="link" href="../intrinsic/functions/has_key.html" title="has_key"><code class="computeroutput"><span class="identifier">has_key</span></code></a>.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><a class="link" href="../intrinsic/functions/at_key.html" title="at_key"><code class="computeroutput"><span class="identifier">at_key</span></code></a><span class="special">&lt;</span><span class="identifier">K</span><span class="special">&gt;(</span><span class="identifier">s</span><span class="special">)</span></code>
                  </p>
                </td>
<td>
                  <p>
                    The element associated with the key <code class="computeroutput"><span class="identifier">K</span></code>
                    in the sequence <code class="computeroutput"><span class="identifier">s</span></code>;
                    see <a class="link" href="../intrinsic/functions/at.html" title="at"><code class="computeroutput"><span class="identifier">at</span></code></a>.
                  </p>
                </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="fusion.sequence.concepts.associative_sequence.h4"></a>
          <span class="phrase"><a name="fusion.sequence.concepts.associative_sequence.models"></a></span><a class="link" href="associative_sequence.html#fusion.sequence.concepts.associative_sequence.models">Models</a>
        </h6>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              <a class="link" href="../../container/set.html" title="set"><code class="computeroutput"><span class="identifier">set</span></code></a>
            </li>
<li class="listitem">
              <a class="link" href="../../container/map.html" title="map"><code class="computeroutput"><span class="identifier">map</span></code></a>
            </li>
<li class="listitem">
              <a class="link" href="../../view/filter_view.html" title="filter_view"><code class="computeroutput"><span class="identifier">filter_view</span></code></a>
              (where adapted sequence is an <a class="link" href="associative_sequence.html" title="Associative Sequence">Associative
              Sequence</a> and a <a class="link" href="forward_sequence.html" title="Forward Sequence">Forward
              Sequence</a>)
            </li>
<li class="listitem">
              <a class="link" href="../../view/iterator_range.html" title="iterator_range"><code class="computeroutput"><span class="identifier">iterator_range</span></code></a>
              (where adapted iterators are <a class="link" href="../../iterator/concepts/associative_iterator.html" title="Associative Iterator">Associative
              Iterator</a>s)
            </li>
<li class="listitem">
              <a class="link" href="../../view/joint_view.html" title="joint_view"><code class="computeroutput"><span class="identifier">joint_view</span></code></a>
              (where adapted sequences are <a class="link" href="associative_sequence.html" title="Associative Sequence">Associative
              Sequence</a>s and <a class="link" href="forward_sequence.html" title="Forward Sequence">Forward
              Sequence</a>s)
            </li>
<li class="listitem">
              <a class="link" href="../../view/reverse_view.html" title="reverse_view"><code class="computeroutput"><span class="identifier">reverse_view</span></code></a>
              (where adapted sequence is an <a class="link" href="associative_sequence.html" title="Associative Sequence">Associative
              Sequence</a> and a <a class="link" href="bidirectional_sequence.html" title="Bidirectional Sequence">Bidirectional
              Sequence</a>)
            </li>
</ul></div>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2006, 2011, 2012 Joel de Guzman,
      Dan Marsden, Tobias Schwinger<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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